1. FIELD OF THE INVENTION
The present invention relates to a process for annealing a heat fused cast refractory product. More particularly, it relates to a process for annealing a heat fused cast refractory material in a mold which is held in a heat insulating material by directly casting a molten refractory material in said cast mold.
2. DESCRIPTION OF THE PRIOR ART
The heat fused cast refractory product (hereinafter referring to as a cast product) is obtained by heat-fusing a refractory material made of desired components in an electric furnace, casting the molten refractory material in a mold having a desired shape and annealing the heat fused cast refractory product.
As the annealing process, it has been mainly employed to anneal a molten refractory material in a mold or a hot cast product taken out of a mold by holding it in a heat insulating material as an annealing medium such as diatomaceous earth powder, alumina powder, sand and chamotto grain as disclosed in U.S. Pat. Nos. 2,154,153; 2,079,101 and Japanese Patent Publication No. 24081/1978. Such annealing processes have serious disadvantages that a lot of dust is generated and an operation is carried out at high temperature to cause serious bad environments in the operation and difficulty for improvements by a machine system, because the cast refractory product is buried or taken out from the heat insulating material as an annealing medium in the transferring system.
On the contrary, it has been employed to cast directly a molten refractory material in an assembled mold held in a heat insulating material in a container as disclosed in U.S. Pat. No. 2,154,153. For example, this process can be employed for a cast product in a system using a graphite mold. This process, however, has not been employed in a system using a sand mold as a casting mold such as a product of a zirconia-alumina-silica type or alumina-silica type cast product, because a mechanical strength of the sand mold is not high enough. It has been proposed to support the sand mold from the rear surfaces by a supporting material as described in Japanese Examined Patent Publication No. 29172/1976, however, such process has required complicated steps. Even though such process is employed, the mold is only partially held whereby it is not enough to prevent breaking of the sand mold in the casting operation.